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olivierd098 avatar image
olivierd098 asked

Smart BMS 12-200: how to detect A-B11 undervoltage

Hi, I'm learning about the Victron ecosystem. As I understand it so far:

  • The error A-B11 for undervoltage comes later than the load disconnect is triggered, when the batteries are further discharged.
  • When the load disconnect is first triggered, charging is still allowed.
  • The BMS will allow charging (as long as the batteries are warm enough) until A-B11 is triggered.
  • The charge disconnect signal only triggers for overvoltage, not undervoltage.

If the above is correct, is there a way to detect A-B11, or the fact that BMS is not allowing charging specifically because of undervoltage? I am trying to understand how it was achieved in this video. One of their Orion is used for trickle charging the battery (at 0.1A then 0.1C until the battery recovers) and is only activated in case the BMS disallows charging/is completely shut off. I wonder how to detect this to achieve a similar setup. Thank you!

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klim8skeptic avatar image
klim8skeptic answered ·

@olivierd098 The error A-B11 for undervoltage comes later than the load disconnect is triggered, when the batteries are further discharged.

No. Once the A-B11 voltage limit has been passed, loads have been disabled. You will get a pre alarm warning W-B12 before the lights go out.

When the load disconnect is first triggered, charging is still allowed.

Yes.

The charge disconnect signal only triggers for overvoltage, not undervoltage.

ATC will also be disabled when the battery is too cold, or too hot.

If the above is correct, is there a way to detect A-B11, or the fact that BMS is not allowing charging specifically because of undervoltage?

A-B11 is very specific. Battery (Cell) under voltage. A-B15 is the alarm for batt over temp (and probably for batt under temp, same battery bTv signal)

Smart BMS 12-200manual.


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olivierd098 avatar image olivierd098 commented ·

Thank you for the answer. Then, if I have do end up having A-B11 (e.g. from some parasitic loads), I would need to follow the "Charge procedure for recovery after low voltage event", right? Is it ok to leave the alternator connected to the BMS charge port during this step, or does it have to be disconnected while the BMS controls a separate charger for the recovery procedure? The manual mentions that an external charger (controlled by the BMS) needs to be used, but I can't find whether the battery needs to be disconnected from the BMS.

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